Nathaniel Chaisson, a cementing-service coordinator for Halliburton, testified that BP went with six centralizers -- used to keep the drill pipe centered in the well as the cement is poured -- instead of the 21 recommended by Halliburton engineers.

Chaisson was called as Halliburton's first witness in the fifth week of the Gulf oil spill trial. He worked as a well technician at the time of the accident and was on the rig from April 16 until April 20, 2010, the day of the Macondo blowout.

Chaisson testified Wednesday that he learned about BP's decision to use fewer centralizers from BP engineer Brian Morel and
well-site leader Donald Vidrine once he was on the rig.

"I was under the impression going out to the rig that there were going
to be 21 centralizers on the casing. I later learned while being on the
rig that a decision had been made not to run 15 additional centralizers
and run only six," Chaisson testified during direct examination by
Halliburton lawyer Bruce Bowman.

In turn, Chaisson said, he called Jesse Gagliano, a
Halliburton technical adviser who worked in the same office in Houston
with the BP engineers.

"He seemed a bit upset about the decision," Chaisson testified. "He said that there had been some
previous talks during the design phase of the job, and that individuals
within BP were aware of, I guess, the impact on the cement job."

Gagliano had warned his clients that
day that if the tube wasn't centered, cement poured in the hole could go
toward the wider side, leaving a weaker barrier on the opposite side, previous expert-witness testimony said.

Chaisson testified the decision raised a red flag, but it was not a safety concern, now or at the time, and said using fewer centralizers could mean having to do remedial cement work after the fact. "There was no safety concern," he said. "I was completely aware of the effect it may
potentially have on the cement job, but there were no safety concerns."

"You didn't raise this as a safety issue to Jesse or to anyone on the rig, did you?" BP lawyer Robert "Mike" Brock asked during cross-examination, in an effort to show that personnel of the British oil giant had not sought to push the job on despite safety concerns.

Chaisson testified he did not receive the results of a foam stability test, conducted prior to the cement job to determine the integrity of the material, nor did he ask for them. Chaisson said he assumed Gagliano had run the procedure. "That's typically the first test that is performed when pumping a foam job," he said.

During cross-examination, plaintiffs' lawyer Jeffrey Breit asked Chaisson about earlier testimony from Tim Probert, Halliburton's president for strategy and corporate development, who cast doubt on the integrity of the cement during the third week of the trial.

"If you had been aware of the fact this particular cement slurry had a low probability of success, you would not have pumped it, would you?" Breit asked.

"I would have raised some red flags. It would have raised a flag in my mind, yes," Chaisson testified.

The issue of centralizers became a focus during the August 2010 joint hearings by the U.S. Coast Guard and the Bureau of Ocean
Energy Management, Regulation and Enforcement, which were held to investigate the causes
of BP's Macondo well blowout.

Transocean's Deepwater Horizon rig caught fire and exploded April 20, 2010, killing 11 workers and leading to one of the largest oil spills in the nation's history.

BP operated the Macondo well, and Transocean owned and manned the Deepwater Horizon drilling rig. For BP and the other companies, the first phase of the complex court case will assign liability for the accident and focus on whether the actions of the companies involved leading up to the accident constitute gross negligence or willful misconduct.

U.S. District Court Judge Carl Barbier is trying the case without a jury.

Plaintiffs' attorneys also rested their case March 20. Lawyers for Transocean presented their defense second and wrapped up Tuesday.

Testimony continued into the afternoon Wednesday from Richard Strickland, an expert-witness called by Halliburton to discuss hydrocarbon bearing zones. Strickland, a petroleum engineer and consultant, runs his own firm and specializes in engineering and geological analysis of oil fields for major oil companies.